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EN
Suspensions of nano-scale particles in liquids, dubbed nanofluids, are of great interest for heat transfer applications. Nanofluids potentially offer superior thermal conductivity to alternative, pure fluids and are of particular interest in applications where active cooling of power-dense systems is required. In this work, the thermophysical properties of carbon nanotube nanofluids (CNTNf) and those of graphene nanoplatelette nanofluids (GNPNf) as functions of particle volume fraction are deduced from published experiments. These properties are applied to a perturbative boundary layer model to examine how the velocity and temperature profiles (and correspondingly shear stress and surface heat transfer) vary with the nanoparticle concentration in the entrance region of microchannels. Findings of this modeling effort indicate that both shear stress and heat transfer in GNPNf increase with increasing particle concentration. The normalized increase in shear stress is approximately twice that for heat transfer as a function of the GNP particle concentration. Interestingly, CNTNf shows anti-enhancement heat transfer behaviour; an increasing concentration of CNT nanoparticles is associated with both an increase in shear stress and a decrease in the surface heat transfer rate.
Open Physics
|
2013
|
tom 11
|
nr 12
1694-1703
EN
This paper deals with the boundary layer flow and heat transfer of nanofluids over a stretching wedge with velocity-slip boundary conditions. In this analysis, Hall effect and Joule heating are taken into consideration. Four different types of water-base nanofluids containing copper (Cu), silver (Ag), alumina (Al2O3), and titania (TiO2) nanoparticles are analyzed. The partial differential equations governing the flow and temperature fields are converted into a system of nonlinear ordinary differential equations using a similarity transformation. The resulting similarity equations are then solved by using the shooting technique along with the fourth order Runge-Kutta method. The effects of types of nanoparticles, the volume fraction of nanoparticles, the magnetic parameter, the Hall parameter, the wedge angle parameter, and the velocityslip parameter on the velocity and temperature fields are discussed and presented graphically, respectively.
EN
Experimental investigation of heat transfer during pool boiling of two nanofluids, i.e. water-Al2O3 and water-Cu has been carried out. Nanoparticles were tested at the concentration of 0.01%, 0.1%, and 1% by weight. The horizontal smooth stainless steel tubes having 10 mm OD and 0.6 mm wall thickness formed the test heater. The experiments have been performed to establish the influence of nanofluids concentration on heat transfer characteristics during boiling at different absolute operating pressure values, i.e. 200 kPa, ca. 100 kPa (atmospheric pressure) and 10 kPa. It was established that independent of nanoparticle materials (Al2O3 and Cu) and their concentration, an increase of operating pressure enhances heat transfer. Generally, independent of operating pressure, sub- and atmospheric pressure, and overpressure, an increase of nanoparticle concentration caused heat transfer augmentation.
EN
This paper deals with the change in contact angle of droplets for three nanofluids, i.e., water- Al2O3, water-TiO2 and water-Cu. Nanoparticles were tested at the concentration of 0.01, 0.1, and 1% by weight. Although dispersants were not used to stabilize the suspension, the solutions tested exhibited satisfactory stability. Ultrasonic vibration was used in order to stabilise the dispersion of the nanoparticles. Experimental measurements were performed for horizontal stainless steel (316) tube of three diameters, i.e., 1.6, 3 and 5 mm, and flat stainless steel plates. The results obtained show that the contact angle of tested nanofluids depends strongly on nanoparticle concentration as well as the curvature of the substrate.
EN
The continuum formulation is applied to the developing boundary layer problem, which approximates the entrance region of nanofluid flow in micro channels or tubes. The thermophysical properties are expressed as “equations of state” as functions of the local nanofluid volume fraction. Based on experimental utilization of nanofluid prevalently at small volume fraction of nanoparticles, a simple perturbation procedure is used to expand dependent variables in ascending powers of the volume fraction. The zeroth order problems are the Blasius velocity boundary layer and the Pohlhausen thermal boundary layer. These are accompanied by the volume fraction diffusion equation. In detailed applications, the boundary condition of zero-volume flux at a solid wall is specified and yields an “insulated wall” solution of constant volume fraction. Two property cases are calculated as comparisons: one is the use of mixture properties for the nanofluid density and heat capacity and the transport properties prevalently used in the literature attributed to Einstein and to Maxwell. Results for alumina are compared to experiments. The theory underestimates the experimental results. This leads to the second comparison, between “conventional” properties and those obtained from molecular dynamics computations available for gold-water nanofluids. The latter properties considerably increased the heat transfer enhancement relative to “conventional” properties and heat transfer enhancement is comparable to the enhanced skin friction rise. To fully appreciate the potential of nanofluids and heat transfer enhancement, further molecular dynamics computations of properties of nanofluids, including transport properties, accompanied by careful laboratory experiments on velocity and temperature profiles are suggested.
EN
Water and ethylene glycol as ordinary coolants have been broadly utilized as a part of a car radiator for a long time. These heat exchange liquids offer low thermal conductivity. With the progression of nanotechnology, the new era of heat transfer fluids called, “nanofluids” have been developed and analysts found that these liquids offer higher thermal conductivity contrasted with that of routine coolants. This study concentrated on the utilization of a mixture of water and ethylene glycol based Al2O3 nanofluids in a cooling framework. Pertinent information, nanofluid properties and exact connections were obtained from literature review to examine the performance of a twin cylinder Diesel engine under various blends of nanofluid based coolants, furthermore, to research heat exchange improvement of a car radiator worked with nanofluid-based coolants. It was observed that, the performance of Diesel engine and heat transfer rate in cooling system framework enhanced with the utilization of nanofluids (with water and ethylene glycol the basefluid) contrasted with water and ethylene glycol (i.e. base liquid) alone. In the wake of leading the series of tests on Twin cylinder Diesel engine at 2%, 1% and 0.5% of nanofluid in basefluid, it was observed that performance of Diesel engine and heat exchange is upgraded better at 0.5% of Al2O3 nanofluid coolant.
EN
The main goal of this study was to perform the neutronic analysis of nanofluids as a coolant in reactor simulation. The variation of multiplication factor and thermal power have been investigated in the Bushehr VVER-1000 reactor core with using different nanofluids as coolant. In the applied analysis, water-based nanofluids containing various volume fractions of Al2O3, TiO2, CuO and Cu nanoparticles were used. The addition of different types and volume fractions of nanoparticles were found to have various effects on reactor neutronic characteristics. By using WIMS-D5 and CITATION code, the appropriate nanofluid with optimum volume percentage of nanoparticles was achieved. The results show that at low concentration (0.1% volume fraction) alumina is the optimum nanoparticle for normal reactor operation.
EN
The multi criterion decision making (MCDM) method and experimental investigation on free convective heat transfer performance of oxide-based water nanofluids along a vertical cylinder are the two methods used to compare the performance in this paper. Al2O3, CuO, TiO2, SiO2, Fe3O4, and ZnO were the metal oxide nanoparticles used in the study to make water-based metal oxide nanofluids with volume fractions ranging from 0% to 1%. Two step method was used to create nanofluids. Thermo-physical properties like density, specific heat, viscosity, and thermal conductivity were measured after the various nanofluids were synthesized. Then, the performance of each nanofluid was evaluated based on various attributes using the weighted sum model (WSM) method, and the ranking of nanofluids was given. To begin, water served as the medium for free convection heat transfer experiments to validate the experimental setup. Free convection heat transfer experiments were carried out using metal oxide-based water nanofluids as mediums at volume fractions ranging from 0% to 1% for various heat inputs in the range of 30 W and 50 W. The heat transfer coefficient augments with percentage volume concentration up to 0.1 % for all types of nanofluids and then decreases until it reaches 0.6% volume fraction. Al2O3-water nanofluid performs better than other metal oxide nanofluids in both WSM and experimental methods.
EN
The main aim of this paper is to improve the heat transfer in a square cavity with a body at the left wall filled with a Al2O3/water nanofluid for different geometries. Numerous simulation experiments are conducted. A relative temperature is maintained at the vertical and top horizontal walls while the bottom wall is warm. The finite volume approach is considered to resolve the equations governing the thermal transfer flow in the physical domain based on the SIMPLER algorithm. In this study, different values of the following parameters are considered: Rayleigh number (104 ≤ Ra ≤ 105) and solid volume fraction (0 ≤ φ ≤ 0.1) of nanoparticles (NPs). Parameters, such as the Rayleigh (Ra) and Bejan (Be) numbers, thermal conductivity, body’s dimensions, and NPs volume fraction, which directly affect the entropy generation and heat transfer rate, are studied in a particular way. The obtained results show that entropy generation goes ahead with the Ra increase and inverse to the solid volume fraction increase. One can notice that the heat transfer has a proportional relation with φ and Ra.
EN
In this experimental investigation, the critical heat flux (CHF) of aqua-based multiwalled carbon nanotube (MWCNT) nanofluids at three different volumetric concentrations 0.2%, 0.6%, and 0.8% were prepared, and the test results were compared with deionized water. Different characterization techniques, including X-ray diffraction, scanning electron microscopy and Fourier transform infrared, were used to estimate the size, surface morphology, agglomeration size and chemical nature of MWCNT. The thermal conductivity and viscosity of the MWCNT at three different volumetric concentrations was measured at a different temperature, and results were compared with deionized water. Although, MWCNT-deionized water nanofluid showed superior performance in heat transfer coefficient as compared to the base fluid. However, the results proved that the critical heat flux is increased with an increase in concentrations of nanofluids.
EN
In this paper, magnetohydrodynamic flow (MHD) of a nonofluid over a stretching cylinder is investigated numerically. The Differential Quadrature Method (DQM) is applied for solving the governing equations. The influence of relevant parameters such as the magnetic parameter, the solid volume fraction of nanoparticles and the type of nanofluid on the flow, heat transfer, Nusselt number and skin friction coefficient is discussed. Also, comparison with the published results is presented. The results show that the Nusselt number increases with growth in the volume fraction coefficient and Reynolds number but decreases with the magnetic parameter.
PL
W pracy dokonano przeglądu literaturowego istniejących formuł analitycznych dla określenia przewodnictwa cieplnego nanopłynów. Stwierdzono, że pomimo znacznego wysiłku nie udało się uzyskać wzorów ogólnych o zadowalającej dokładności. Uzyskano natomiast szereg wzorów godnych zalecenia dla konkretnych przypadków szczególnych. Słowa kluczowe: współczynnik przewodzenia ciepła, metody obliczeniowe, nanopłyny
EN
The paper presents literature survey on analytical prediction of effective thermal conductivity of nanofluids. It was found that regardless big efforts a general formula of sufficient accuracy was not obtained. However, a number of trusted in specific cases equations were obtained.
PL
Przedstawiono efekty badań dotyczących spadku ciśnienia przy przepływie nanopłynu przez kanał o malej średnicy. Wyniki eksperymentalne porównano z rezultatami symulacji z wykorzystaniem numerycznej mechaniki płynów (CFD). Zbadano przepływ nanocząstek tlenku miedzi zawieszonych w wodzie przez przewód cylindryczny o średnicy 12 mm. W symulacjach wykorzystano zarówno podejście jednofazowe jak i wielofazowe. Wykazano, iż oba sposoby prowadzenia symulacji dały podobne rezultaty.
EN
The research concerning nanofluid pressure drop during flow through a small diameter pipe is presented. Experimental results are compared with the computational fluid dynamics (CFD) simulations. The flow of copper nanoparticles suspended in water through the cylindrical tube of 12 mm diameter was investigated. In simulations single-phase as well as multiphase approaches were employed. It was proven that both ways of simulations gave similar results.
EN
We report results of rheological experiments on suspensions of nanopowders. In this work we have used two ceramic nanopowders such as magnesium-aluminum spinel (S30CR Baikowski – MgAl2O4) and yttrium oxide (Y2O3) suspended in ethyl alcohol. Rheological studies have been carried out using several experimental systems including Haake Mars 2 rheometer (Thermo Electron Corporation, Karlsruhe, Germany) and Rheo-NMR (Bruker BioSpin, Rheinstetten, Germany). Measurements of dynamic viscosity in the range of shear rates from 0,01 s-1 to 2000 s-1 and the temperature range from -15°C to 20°C has been conducted. Most of the samples exhibited a non-Newtonian nature.
20
75%
PL
Coraz większe zapotrzebowanie na ropę naftową oraz jej wysoka cena rynkowa powodują zainteresowanie zagadnieniami jak najlepszego wykorzystania jej zasobów, także tych niedających się wyeksploatować tradycyjnymi metodami. W związku z tym doskonalenie ulepszonych metod eksploatacji EOR jest dziś jednym z najważniejszych zadań w zakresie kopalnictwa naftowego. Dlatego w niniejszym artykule zaprezentowano badania, które miały na celu sprawdzenie potencjalnych możliwości działania dostępnych na rynku nowych środków do nawadniania na bazie nanocząsteczek. Wstępne analizy wykazały, że dla cieczy z dodatkiem każdego z badanych środków następowało zwiększenie odzysku ropy w porównaniu z nawadnianiem przy użyciu solanki.
EN
The increase in worldwide energy demand and price causes increasing interest in making the best use of oil resources, including those which could not be exploited by traditional methods. Consequently, the improvement of the EOR processes is today one of the most important tasks in the field of oil production. That’s why, this article presents a laboratory study that illustrates the potential usage of nanoproducts or Enhanced Oil Recovery available on the market. Preliminary studies showed that for liquids with the addition of the nanofluids there was an increase in oil recovery compared to the application of brine flooding.
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